Field of the Invention
The present invention relates to a radio communication technique of performing spatial multiplexing.
Description of the Related Art
Recently, the capacity of data transmitted by a wireless network such as a home network or a public network is increasing, the wireless network is congested, and the communication band is tightened. As one means for solving the tightening of the communication band, the IEEE802.11ad standard defines execution of spatial multiplexing (spatial sharing). In spatial multiplexing, two or more pairs each of a transmission node and reception node having directional antennas perform communication in parallel by spatially separating communication links using the directivity characteristics of the antennas so as to satisfactorily reduce the interference between the communication links. Compared to a case in which spatial multiplexing is not performed, the time taken for data transmission can be shortened, and the frequency utilization efficiency of the overall radio communication system can be increased.
When two or more pairs each of a transmission node and reception node perform communication in parallel by spatial multiplexing, the communication period length may differ between the node pairs owing to the difference in the amount of data to be transmitted or the like. At this time, assuming that the communication period length of the first node pair is larger than that of the second node pair, if communication of the second node pair ends, even spatial multiplexing ends. The frequency utilization efficiency may be decreased by that amount.
To solve this problem, Japanese Patent Laid-Open No. 2007-329694 discloses a technique of dividing a communication frame having a large communication period length in accordance with the difference between this communication period length and a smallest communication period length among the communication period lengths of frames to undergo spatial multiplexing, and compensating for the difference in communication period length. Japanese Patent Laid-Open No. 2010-263488 discloses a technique of controlling signal frequency bandwidths used in respective frames in order to make the communication period lengths of the plurality of frames to undergo spatial multiplexing coincide with each other.
In Japanese Patent Laid-Open Nos. 2007-329694 and 2010-263488, the interference of a signal transmitted by the first pair of a transmission node and reception node with communication of the second pair of a transmission node and reception node is not taken into account. That is, Japanese Patent Laid-Open Nos. 2007-329694 and 2010-263488 only describe control of the communication period length on the premise that separation of communication links by the space has been completed. However, the separation performance of communication links by the space depends on the antenna characteristic, the positions of nodes, and the like. In some cases, a signal transmitted by one communication link may interfere with another communication link. In this case, communication by any communication link may fail, decreasing the frequency utilization efficiency.
The present invention increases the frequency utilization efficiency by effectively using the space and time resources based on the communication quality in a radio communication system that performs spatial multiplexing.